Electronic components and integrated circuit packages are often mounted on printed circuit cards creating an electronic assembly of irregularly shaped packages bonded on a planer surface. Multiple circuit cards may be placed into an array (referred to as a "cardcage") within an electronic enclosure thereby maximizing the packaging volume efficiency. Several types and configurations of electronic enclosures with the ability to support various numbers of circuit cards are readily available for connecting the circuit cards into a cardcage. Standard bus architectures have been defined for these cardcages. For example, the VME bus standard (ANSI/IEEE Std. 1014-1987) has been defined for the backplane bus interface for cardcages. Other bus standards include the VME64 Standard, which revises the VME bus standard into a 64-bit architecture, and the VXI ("VME eXtensions for Instrumentation") bus, which is designed to allow low level signals to co-exist on a backplane with high speed digital and RF or microwave signals.
Currently available cardcages have significant complexity due to the number of components and fasteners used for assembly. These cardcages have typically been manufactured using four or five extruded metal rails and sheets, often aluminum, stamped and formed to the shape required to build the cardcage. The extruded rail design requires a pair of rails located at the inlet and exit of the cardcage. These rail extrusions are machined to length, which requires extreme precision to ensure accuracy. The sheets and rails are connected to each other by a suitable means, including rivets, screws, welds, or glue. A card guide is connected between each pair of rails for receiving a circuit card assembly into the cardcage. Both entrance and exit rails must be exact mirror images to ensure proper alignment of the card guides. The card guides are installed by snapping a plastic tab into an oval type slot in the extrusion. The card guides are usually mounted to the extrusion, through a mechanical means, such as screws, for holding them in place. The slots in the rail extrusions, which are used to locate the guides, are typically on 0.20" centers. This spacing requires any card pitch changes (i.e., changes in the card spacing), to be limited to 0.20" increments.
Next, a floating nutrail is slid into each extrusion to provide a means of attaching the associated cards and backplanes. Insulating strips must then be positioned between the backplane and the mounting surfaces prior to backplane attachment.
It has been recognized that this assembly process may be costly and time consuming due to the number of parts and connectors that must be used to connect the components and the complexity involved in aligning the various components. In particular, currently available cardcages require careful alignment of an associated backplane to ensure proper mating of the circuit cards with the backplane. In addition, the cardcage rail extrusion design requires significant tooling costs to produce the intricate features used to ensure proper alignment.
It has also been recognized that an extruded rail design may be deformed when placed under a moderate mechanical loading. The final cardcage assembly of an extruded rail design has a reduced structural integrity due to the number of parts and fastener locations that produce stress concentrations. Therefore, currently available cardcages are susceptible to deflection from a rectangular shape when forces are applied to the sides of the cardcage.
In addition, an extruded rail design does not lend itself to moderate changes or modifications due to the nature of the cardcage design. There is typically one mounting hole on each end of the extruded rails for attachment to the cardcage ends. These mounting holes are located in the extrusion and any change to the mounting holes would require significant tooling costs.
It has further been recognized that cardcages using sheets and extruded metal rails reduce the available airflow through the cardcage due to large obstructions present in the design. Cooling of the circuit cards is further hindered due to restrictive openings and blockage of airflow at the cardcage comers, which results in uneven distribution of air into a cardcage. Cooling of circuit cards in the cardcage is important for proper operation of electronic components on the circuit cards. As circuit cards are being developed with greater electronic component density per card, and electronic components continue to operate at higher frequencies and increased power, the cooling of circuit cards in these electronic enclosures becomes more critical for proper operation of these electronic components. Electronic components that operate above recommended thermal constraints may operate unreliably and cause circuit cards to prematurely fail due to thermal stress. The amount of cooling provided by an airflow source in a cardcage, such as an axial flow fan or a centrifugal blower, is based directly upon the velocity, temperature, and pressure of air provided over the components. If the circuit cardcage hinders airflow from the source due to restrictive openings, then total volumetric airflow is reduced, recirculation loops are created in the cardcage, and low velocity areas occur. As a result, the amount of cooling provided by the airflow source will decrease. Additionally, air that is not distributed evenly into a card slot by the cardcage will not cool all devices on the card evenly and adequately.
It has also been recognized that cardcage designs do not account for the problems associated with the use of multiple fans in front of a cardcage. The use of multiple fans in a cardcage causes significant disturbances in airflow due to the interactions of air from one fan interacting with air from an adjacent fan.
Therefore, there is a need for a cardcage assembly having an integrally formed cardcage side for inlet and exit airflow that reduces the cost and complexity of assembling a cardcage while increasing structural integrity. In addition, a need has arisen for a cardcage in which the cardcage sides inherently align circuit cards to a backplane and are not subject to deflection. An additional need exists for a cardcage assembly that provides for improved cooling within the cardcage and reduced airflow disturbances and/or loses.